The present invention relates to a piston pump, in particular to a piston pump used in slip-controlled hydraulic brake systems as defined by the preamble of claim 1.
Such a piston pump, e.g., is known from EP 0 631 050 B1. The piston pump according to this prior art includes a delivery valve and a suction valve, both arranged within a pump housing so that they are separate from each other in terms of location and construction. Moreover, the known delivery and suction valves are assembled within the pump housing one after the other in terms of time and, once assembled, it is no longer possible to test them without a major effort. However, before assembly, it is likewise not readily possible to perform an optimum test of these valves since in such a case the assembled conditions would have to be simulated as accurately as possible and since the valves could be tested only separately.
A ball-type-design delivery valve is known particularly in the context of the examples of embodiments of a known piston pump as disclosed in FIGS. 11 through 19 of EP 0631 050 B1. There, a valve body having the design of a ball is prestressed, with a ring means being used, against a valve seat designed as radial bore. This known delivery valve has disadvantages in that the assembly of the ring means on the valve seat member of the delivery valve requires a major effort and in that its type of fastening is not particularly stable. In this known arrangement it is moreover possible that the ring means twists or is displaced and, thus, the ball slips out of its valve seat or there is a change in the pre-stressing force.
It is an object of the present invention to avoid the disadvantages of prior art and, in particular, to provide a piston pump enabling both the delivery valve and the suction valve to be preassembled and tested before being assembled into a pump housing, i.e., enabling external preassembly and testing.
This inventive task is solved in a generic piston pump in that the delivery valve and the suction valve are provided on a component which can be handled independently.
An essential advantage of the present invention consists in that the inventive design of the delivery and suction valves provides a valve cartridge unit allowing external preassembly and testing. Moreover, it is possible to reduce the number of parts used as well as the rejects of defective units and, consequently, the cost of manufacture. A further advantage of this invention is the fact that the time needed for assembling the inventive piston pump is considerably reduced which likewise means a drop in costs. The constructional combination of delivery valve and suction valve, moreover, results both in space being saved and in an optimum utilization of the space available for the valves within the pump housing. Finally, the constructional combination of delivery and suction valves permits a simple recessing of the valve seat member as no separate valves have to be accommodated within the pump body.
In a preferred embodiment of this invention, the component is fastened within the pump housing by means of caulking or clinching. This type of fastening is beneficial in terms of cost and enables pressure-tight assembly of the component within the pump housing. Further, this restricts the possibilities of inexpert manipulation of the brake system.
So as to reduce the number of parts required for assembling the component it is an advantage to provide one spring element for jointly prestressing the delivery valve and the suction valve. This spring element may have the design of a compression spring or of a tension spring.
Advantageously, the component includes a valve seat member wherein there is provided a valve seat for the delivery valve and a valve seat for the suction valve. This results in an especially space-and-material-saving design of the component of the inventive piston pump.
According to a further embodiment of this invention, the piston pump includes a cup-shaped pump piston, with the component including an axially projecting gudgeon portion wherethrough the cup-shaped piston is guided. An advantage of this embodiment is the fact that the pump housing does not have to undergo hardening or anodizing.
Advantageously this component includes a valve seat member with an axial recess formed on one of its front sides for guiding the pump piston of the piston pump therein or rather for having it plunge into this recess. Preferably, the suction valve is arranged on the other, opposite front side of the valve seat member essentially axially to the center line of the valve seat member while the delivery valve is arranged essentially radially to said line. This arrangement is particularly space-saving as the pump piston, together with its resetting spring, can plunge into the recess whereby the length of the bore wherein the pump piston moves is shortened.
According to a variant of this invention, the suction valve includes a compression spring secured by means of a bowl-type spring retainer provided with a stop formed thereon for the valve body of the suction valve and further including means for guiding the compression spring and means for guiding a piston return spring serving to reset the piston. The bowl-type spring retainer thus combines a plurality of different functions which means a saving of space and material. Further, the design of the stop for the suction valve body prevents the suction valve body from becoming jammed within the bowl-type spring retainer.
Advantageously, the means for guiding the compression spring and the means for guiding the piston return spring form a cup-shaped portion of the bowl-type spring retainer, with the compression spring being guided on the inside of the cup-shaped portion and the piston return spring being guided on the outside of the cup-shaped portion. The stop of the bowl-type spring retainer preferably serves as an internal guideway for the compression spring. This is particularly beneficial since the bowl-type spring retainer, due to its function as a retaining cage for the suction valve body, is anyway concave, i.e., provided with a cup-shaped portion and since, further, the bowl-type spring retainer anyway includes a stop in order to prevent the suction valve closure member from becoming jammed within the bowl-type spring retainer.
In accordance with this invention, further provided is a delivery valve with a valve seat member, in particular for a piston pump, with a valve body of the delivery valve being prestressed by a clamping element, mountable to the valve seat member, against a valve seat formed within the valve seat member. Particularly advantageous is the fact that the clamping element includes a tongue which is formed thereon and prestresses the valve body against the valve seat. The use of this inventive tongue instead of, for instance, a helical spring is possible because the opening pressure of the delivery valve does not have to be adjusted as accurately as that of the suction valve. It is thus possible to substitute the helical spring in the delivery valve for a tongue provided on the clamping element. The tongue urges the valve body perpendicularly onto the valve seat while simultaneously fixing the valve body axially and radially. Fixation of the valve body may even be improved by means of a bore which can additionally be provided within the tongue and at least partially is engaged by the valve body. Further, the arrangement of the tongue on the clamping element also offers the advantage of adjustability of the resiliency over the length of the tongue, even with a predetermined construction of the valve body. Finally, the arrangement of the tongue within the clamping element offers sufficient surface contact between the clamping element and the valve seat member, namely by means of the surfaces adjoining the tongue, whereby the clamping element can much better be fastened on the valve seat member.
Preferably, the clamping element has a tab, provided perpendicularly to the tongue, for fastening the clamping element on the valve seat member. Thus it is possible to a great extent to prevent the clamping element from twisting and getting loose.
In a preferred embodiment of this invention, the clamping element includes at least one tab, provided parallel to the tongue, for fastening the clamping element in a valve seat member recess serving to receive the valve body. This does not require a separate bore in the valve seat member for fastening the tab.
If the clamping element is dimensioned considerably wider than the valve body, the larger contact surface between clamping element and valve seat member results in an improved fastening of the clamping element on the valve seat member because of only the tension of the clamping element.
So as to facilitate the radial slipping-on of the clamping element onto the valve seat member the cross sides of the clamping element preferably include end portions arched outwards. Slipping-on, however, may also be done axially, starting from an end portion of the valve seat member.